Techniques that allow for rapid and precise, nondestructive parametric measurements are in high demand in the semiconductor industry. Due to the increasing market for semiconductor devices, high volume production is a pressing requirement of semiconductor manufacturers. High volume production presents a challenge in today's technology which requires complicated designs of complex semiconductors. Particularly challenging is the quality control aspect of such high volume manufacturing. Parametric measurements become increasingly important in order to properly and accurately manufacture complex semiconductor designs. Such parameters include counts of impurities, and atmospheric factors including humidity, temperature, and pressure which can directly affect the quality of the manufactured semiconductor as well as the processing time and yield of the manufactured product.
The demands for rapid production of semiconductors adhering to a strict quality control standards often involve differing objectives, all of which must be matched in order to produce a quality product at a high rate and at a relatively low price per part. Balancing these objectives is paramount in order to be competitive in the current semiconductor marketplace.
Producing semiconductor parts at an ever-increasing rate becomes increasingly important as the price per pan is further reduced. Thus, advances in increasing production speed are greatly sought after. A significant amount of time is used in quality control testing during the manufacturing process, particularly where the production rate must be halted or otherwise ceased while such quality control testing takes place. It would be an advance in the art to provide such testing during the production process without halting the forward progress of the processing steps. By simultaneously conducting both manufacturing and quality control steps, the overall throughput and the production volume rate are enhanced. Parametric measurement techniques which can be used during production steps are thus desirable.
Temperature measurement of wafers in semiconductor manufacturing, as presently known in Rapid Thermal Processing (RTP), does not lend itself to the aforedescribed objectives. Thermocouple temperature measurement is impractical at high volume production because it involves direct contact and instrumenting of the wafer. Thus, it is destructive, expensive, and not very repeatable.
The calibration technique of pyrometry involves heating a sample to a known temperature and involves setting the temperature output by the pyrometer according to the temperature. This calibration technique is somewhat inaccurate because of the emissivity variation of the backside of a semiconductor and it is difficult and challenging to obtain consistent results therefrom.
Pyrometric measurement of wafer temperature is a very strong function of wafer emissivity and has an induced drift in temperature such that accuracy and repeatability of temperature measurement is very difficult to accomplish. Ion deposition and plasma etching steps in wafer fabrication processes do not lend themselves to temperature measurement techniques currently being used, and these techniques are particularly problematic when being used in situ.
It is desirable to have a closed loop temperature control mechanism such that the temperature in heat treatment of wafers during manufacturing can be adjusted according to a feedback of how wafers are being affected during the heat treatment. Accordingly, it would be advantageous to derive a temperature measurement and calibration technique which is nondestructive, non-contact, accurate, and unobtrusive in the environments known to wafer processing systems, such as vacuum environments. The reflectance method proposed in the current invention meets all these criteria and is very suitable in production environments.